1. Field of the Invention
The invention relates to high capacity electrode active material which is mainly an amorphous transition metal complex represented by AxMPyOz, and a manufacturing method of that electrode active material.
2. Description of the Related Art
A secondary battery is known which charges and discharges by cations such as lithium ions traveling between electrodes. One classic example of such a secondary battery is a lithium-ion secondary battery. Material that can absorb and release lithium ions can be used for the electrode active material of such a secondary battery. One example of such material is carbonaceous material such as graphite which is an example of negative electrode active material. On the other hand, an example of positive electrode active material is an oxide which has lithium and a transition metal as constituent elements, such as lithium nickel oxide or lithium cobalt oxide (hereinafter, such an oxide may also be referred to as a “lithium-containing composite oxide”). Moreover, in recent years, chemical compounds having an olivine structure, e.g., chemical compounds represented by the general expression LiMPO4 (M=Mn, Fe, Co, Cu, V), are promising for positive electrode active material due in part to their large theoretical capacity.
Meanwhile, Japanese Patent Application Publication No. 2005-158673 (JP-A-2005-158673) describes electrode active material which is mainly an amorphous metal-phosphate complex that has an olivine structure. With the electrode active material that is mainly a metal-phosphate complex, an amorphous body can be synthesized from an inexpensive metal oxide at an extremely low cost and in a short period of time by rapid cooling compared with a crystalline body of related art. What is more, the resultant amorphous body seems to display the same battery properties as the crystalline body.
However, electrode active material that is mainly an amorphous metal-phosphate complex is not able to realize its theoretical capacity. As a result, its capacity remains small so the desired charging and discharging characteristics are unable to be obtained.
EP-A2-1,193,787 and US 2004/0033360discloses an LiFePo 4 carbon composite material which is prepared by mixing various reactants and amorphous carbon material and milling the reactants using a planatory ball mill. The milled mixture is then sintered prior to being cooled.